1. Field of the Invention
The present invention relates to an improved apparatus for the low pressure chemical vapor deposition (LPCVD) of thin silicon films, including polysilicon, SiO.sub.2, Si.sub.3 N.sub.4, silicon oxynitride and related materials, hereinafter referred to as silicon films, onto substrates such as device wafers or semiconductor bodies, and/or for the selective etching of lithographic patterns in such thin films, such as during the production of semiconductor circuits, and to processes for making and using same.
Conventional devices used for the LPCVD process contain a cylindrical reaction chamber, tube or belljar into which the substrate to be coated and/or etched is inserted and into which the vapor-forming gases are supplied. The reaction chamber commonly comprises an elongate tube or cylinder of quartz (SiO.sub.2) ceramic or of fused quartz and contains or communicates with a heater for reacting and decomposing the vapor-forming deposition gases, to cause the low pressure deposition of a desired silicon layer onto the substrate and/or a high frequency inducing means for forming an etchant plasma from etchant gases to cause plasma etching and removal of portions of a silicon layer from the substrate.
However, the LPCVD of silicon layers within a CVD reaction chamber causes the Silicon film to deposit on and coat the quartz wall of the reaction chamber. Deposited silicon layer wall coatings become thick and crack and flake after several deposition cycles, producing contamination requiring periodic removal and cleaning of the reactor wall or tube. This is time-consuming and requires shut-down of the apparatus. In the case of etchant gases, such as CF.sub.4 /O.sub.2, SF.sub.6 /O.sub.2 and NF.sub.3, such gases attack and etch away the quartz wall of the reaction chamber during repeated use and require eventual replacement thereof.
2. Discussion of the Prior Art
U.S. Pat. No. 4,529,474 discloses a method for cleaning silicon deposits from the walls of CVD reaction chambers, in-situ without removing the reaction chamber wall from the apparatus, by etching such deposits from the chamber wall using CF.sub.4 /O.sub.2 plasma as an etchant gas. Such a method is useless in cases where the reactor wall or tube is susceptible to being etched or corroded by fluorine-containing gases, as in the case of SiO.sub.2 walls such as quartz.
U.S. Pat. No. 4,707,210 discloses a CVD apparatus having an aluminum reactor wall in place of a stainless steel reactor wall, to overcome the problem of corrosion of the stainless steel reactor wall by fluorine-containing etchant gases. However, aluminum reactor walls are not resistant to temperatures above about 600.degree. C., which temperatures are frequently reached in the LPCVD process for producing semiconductors. Any sublimation of aluminum within the reaction chamber produces unacceptable contamination of the substrate being coated and eventful destruction of the wall.
U.S. Pat. No. 4,633,812 discloses a CVD apparatus having reactor wall portions which are resistant to corrosion by fluorine-containing gas plasma, characterized by the use of a reactor wall consisting of a sintered dielectric wall material of alumina ceramic. While such alumina ceramic portions wall are highly resistant to corrosion by fluorine-containing etching gases, they are not ideal for vacuum processes because they are not very dense and are somewhat porous, and they cannot be formed to have integral flanges, as is possible with fused quartz.